The present invention is directed to an aluminum electrolyte capacitor composed of wound layers of two aluminum foils, the foil serving as an anode is provided with an oxide layer acting as dielectric, wherein the anode foil can be potentially produced by parting from a larger shaped foil web, spacers saturated with an operating electrolyte are arranged between the two aluminum foils, and the aluminum foils are contacted with riveted and/or welded power supply terminal strips. The invention is also directed to a method for the manufacture of same.
The electric strength of aluminum electrolyte capacitors is essentially limited by the dielectric oxide layer, the electrolyte, and the spacers (paper, plastic foils or the like). The electrolyte especially is responsible for a critical limitation of the voltage strength, so that increased gas development and arc-overs then arise above the voltage conditioned by the respective operating electrolyte.
This problem can be avoided in that all formatting parts are designed for the high peak voltage. But, this solution results in high costs and, has the disadvantage that one is forced to utilize operating electrolyte having a high sparking voltage that, however, exhibits a low conductivity. Accordingly, the electrical loss properties of the capacitor are significantly deteriorated.
With respect to the peak electric strength, the weak points are the points of the anode at which the anode contacts the electrolyte without a separator layer that boosts the drop resistance. The weak points also include those surfaces that are not provided with a pre-forming layer (for example, cut anode edges, terminal elements).
German Patent No. DE-C 870 587 discloses an electrolyte capacitor wherein the cut edge of the pre-formed foil is provided with a non-conductive coating that is indifferent with respect to the electrolyte. The non-conductive coating is preferably composed of lacquer. A difficulty in this design exists in that only the cut edges are covered, but passages lying in the interior of the winding cannot be inactivated or can only be inactivated with an extremely great outlay.
German Patent No. 29 50 246 A1 further discloses that plastic laminates are arranged above the terminal strip. Large gaps in the capacitor winding are created due to this type of covering. These large gaps lead to a great scattering of the electrical values. The cut edges cannot be inactivated with this method.
German Patent No. 30 04 728 A1 discloses that the power supply terminal strips be provided with a gamma-Al.sub.2 O.sub.3 layer based on a temperature treatment. However, faults at the anode foil cannot be eliminated with this method because the dielectric layer produced by anodic oxidation would be damaged by a temperature treatment.
German Patent No. 14 89 839 A discloses that chemical substances such as barium oxide, strontium oxide, or calcium oxide are added to an electrolyte capacitor in order to weaken or prevent the injurious consequences of moisture in combination with the gases. An inactivation of the edges and voids is not therewith achieved.